1. Field of Invention
The present invention relates to a laser annealing system which prevents damage to a chamber window by inserting a buffer window between the chamber window of a process chamber (hereinafter referred to as a xe2x80x9cchamberxe2x80x9d) and a film which is annealed by a laser.
2. Discussion of Related Art
A laser annealing technology can form a polycrystalline silicon film having high electron mobility by annealing an amorphous silicon film, which is formed on a poor heat-resisting glass substrate with a laser under low temperature. In a laser annealing technology, an amorphous silicon film is formed on a glass substrate at about 300xc2x0 C., hydrogen is released out of the amorphous silicon film by a heat annealing at about 450xc2x0 C., and then the film is irradiated with a laser beam having short pulse duration. An annealing system is used for a laser annealing process in fabricating a liquid crystal display (LCD), more specifically, used for crystallizing or activating a film with a laser.
FIG. 1 shows a prior art schematic diagram of a chamber used in a laser annealing system. Referring to FIG. 1, a chamber wall 11 constituting an outer frame of the chamber provides an inner space in which a substrate supporter 18 is placed for supporting a substrate 20 to be annealed. The drawing shows upper and lower parts of the chamber wall 11. The inner space is exposed through a predetermined portion of the upper part of the chamber wall 11. In particular, the inner space is sealed with a chamber window 13 preferably made of quartz.
The inner space sealed with the chamber wall 11 and the chamber window 13 is maintained under a vacuum state. The chamber window 13 has a thickness over 2 cm so as to withstand the vacuum state. Unfortunately, the chamber window 13 made of quartz is very expensive since the price of the chamber window 13 is directly proportional to its thickness.
The technique of annealing an amorphous silicon film with a laser and the above-mentioned chamber of the laser annealing system is explained by referring to FIGS. 1 and 2. FIG. 2 shows a substrate on which amorphous silicon patterns to be irradiated with a laser are formed. Referring to FIG. 2, predetermined amorphous silicon patterns 21-1 to 21-3 are defined on a substrate 20. The pattern 21-1 is placed in the center of the substrate. The pattern 21-2 is on the left side of the pattern 21-1. The pattern 21-3 is on the upper side of the pattern 21-1. The amorphous silicon patterns 21-2 and 21-3 on the substrate 20 are going to be irradiated with a laser in order to attain polycrystalline silicon from amorphous silicon by crystallization.
A laser annealing is achieved by supporting the substrate 20 on which an amorphous silicon film has been formed on a support 18 in the inner space of the chamber of a laser annealing system, and by having the amorphous film irradiated with a laser beam having its focus fixed from the outside of the chamber through the chamber window 13. In this process, diameters of the laser beams corresponding to the sizes of the patterns have to be set to crystallize the amorphous silicon patterns 21-2 and 21-3. Typically, the amorphous silicon pattern 21-2 is irradiated with a laser beam of which diameter corresponds to the size of the pattern 21-2.
The remaining amorphous silicon pattern 21-3 is irradiated along with the pattern by a laser beam having the corresponding diameter. Namely, the crystallization, the activation and the like are processed by having the surface of the amorphous silicon film irradiated through the chamber window 13 with a laser beam wherein the substrate is placed on the support 18 in the inner space of the chamber. In this case, a portion of the amorphous film may be vaporized when the energy density of the laser beam is excessively larger than is necessary for the thickness of the film. Moreover, the contaminants on the surface of the film which have low evaporation points are vaporized.
Such vaporized components of the film and the contaminants are deposited on the lower surface of the chamber window 13 so that the chamber window 13 is damaged or contaminated. The damage or the contamination on the chamber window 13 also interferes with the laser beam passing through the chamber window 13, thereby causing a low process yield in the laser annealing process. Accordingly, the lower surface of the chamber window 13 under which the contaminants have been deposited needs to be frequently cleaned or polished, or the contaminated chamber window should be replaced with an expensive brand-new one.
Moreover, it is impossible for a laser to be applied to the film in accordance with its pattern as the film is irradiated with the laser directly through the chamber window 13 in the laser annealing system according to prior art. Accordingly, the process takes more time and increasing the process yield becomes complicated since the diameter and the position of the laser beam must be adjusted frequently.
Accordingly, the present invention is directed to a laser annealing system that substantially obviates one or more of the problems due to limitations and disadvantages of the prior art.
The object of the present invention is to provide a laser annealing system which prevents damage on a chamber window by stopping the contaminants being deposited on a chamber window with a buffer window between the chamber window and the film which is irradiated with a laser.
Another object of the present invention is to provide a laser annealing system which defines laser patterns by forming a buffer window to have a predetermined shape.
Additional features and advantages of the invention will be set forth in the description which follows and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the present invention includes a chamber window through which a laser beam passes, a chamber wall constituting an outer frame wherein the chamber wall and the chamber window forming a sealed inner space therein. The laser annealing system further includes a process chamber for annealing the substrate with a laser, and a buffer layer between the chamber window and the substrate. In this case, a pattern of a laser beam passing through the buffer window takes after a predetermined pattern formed on the buffer window.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.